1. Field of the Invention
The present invention relates to a flexible printed circuit board with a reinforcing plate having the excellent washing resistance and mounting resistance.
2. Description of the Related Art
Recently, realization of miniaturization or higher speed has been promoted in the field of the electronic appliances according to the progress of the electronic industry. Therefore, a lightweight flexible printed circuit board capable of packaging a three-dimensional wiring in a narrow space is used in a wider range with a higher demand. Accordingly, flexible printed circuit boards with reinforcing plates, prepared by attaching various kinds of reinforcing plates, such as a reinforcing thick plastic film, an engineering plastic plate, a glass epoxy laminated plate, and a metal plate serving also as a heat radiating plate, on a flexible printed circuit board with an adhesive in a part wherein parts are mounted, or in a part to be inserted in a connector are used frequently, and improvement of the performance thereof is desired.
In view of the circumstances, recently, a flexible printed circuit board with a reinforcing plate with not only the bonding property and the heat resistance but also the solder reflow resistance, the washing resistance, and the mounting resistance (screw fastening, or the like) at the time of packaging (mounting) the parts is called for. However, the conventional flexible printed circuit boards with a reinforcing plate have both advantages and disadvantages in the characteristics, and thus the above-mentioned characteristics are not always satisfied in the real situation.
The invention has been achieved in view of these circumstances, and an object thereof is to provide a flexible printed circuit board with a reinforcing plate having not only the bonding property and the heat resistance but also the excellent solder reflow resistance, washing resistance and mounting resistance at the time of packaging the parts.
In order to achieve the object, a flexible printed circuit board with a reinforcing plate, comprising a flexible printed circuit board having a conductive circuit pattern layer, and an insulating layer made of a plastic film, with a reinforcing plate attached via an adhesive layer, wherein the adhesive layer is provided using a composite metal hydroxide represented by formula (1):
M1-xQx(OH)2xe2x80x83xe2x80x83(1) 
Wherein M is at least one metal atom selected from the group consisting of Mg, Ca, Sn, and Ti, Q is at least one metal atom selected from the group consisting of Mn, Fe, Co, Ni, Cu, and Zn, and x is a positive number from 0.01 to 0.5.
That is, the present inventors have studied elaborately for obtaining a flexible printed circuit board with a reinforcing plate having not only the bonding property and the heat resistance but also the excellent solder reflow resistance, washing resistance and mounting resistance at the time of packaging the parts. Then, they paid attention to the complex modulus of elasticity of the adhesive for the reinforcing plate of the flexible printed circuit board having a reinforcing plate, and further studied with the focus thereon. As a result, they have found out that a 100 MPa or more complex modulus of elasticity at 25xc2x0 C. (generally 3,000 MPa or less as an upper limit) and a 10 MPa or more complex modulus of elasticity at 70xc2x0 C. (generally 300 MPa or less as an upper limit) are preferable. In general, since those having a good peel strength, containing as the main component an epoxy resin-acrylonitrile butadiene rubber (NBR) or epoxy resin-acrylic based polymer component to be used at the time of attaching a reinforcing plate on a flexible printed circuit board have a low glass transition temperature, and a low complex modulus of elasticity, they have poor solder reflow resistance, washing resistance, and mounting resistance, and thus they are not suitable for use as an adhesive for adhering a reinforcing plate and a flexible printed circuit board. In contrast, those having a high glass transition temperature and a high complex modulus of elasticity have a lower peel strength. Moreover, in the conventional technique, usable reinforcing plates are limited. In particular, untreated aluminum plates are disadvantageous because they are not usable due to the poor bonding property. The invention is to solve the problems for providing a flexible printed circuit board with a reinforcing plate having the excellent bonding property as well as the excellent washing property and packaging property.
By setting the content of the composite metal hydroxide in a specific ratio, a desired high complex modulus of elasticity can easily be obtained so that an adhesive composition with a further superior bonding property can be obtained.